A five angle valve job cuts five angles into the valve/valve seat. A valve job like that improves sealing in the cylinder head for one. Secondly, air begins to tumble over about 35 degrees of pitch and wipes out the possibiblity of a nice tulip (swirl of atomized air/fuel) for the best combustion and flame front propegation across the piston when the spark lights it off. When boosting a motor the air is already too turbulent for this tulip, but you are running over 100% volumetric effeciency and that makes up for it, so at that point it is about sealing in all of that pressure. Yes it helps, a shop should be able to help you determine how agressively you need to work over the head. As long as it is off, I would look into mild porting, port matching, and polishing. You will get nice gains from the total package. Don't let a domestic machinest work over your head!!! They will want to hog out your ports like old Domestics and your car will run like shit below 6 grand. Hope this helps.